Multi-layer ceramic capacitors are used for reduced coupling and buffering of the power supplies for processors, and particularly for high-output microprocessors. While operating in a high-output mode, these active electronic components generate a large amount of heat, and the temperature of high-output processors during continuous operation can reach as high as 70 to 80° C. even if subjected to concentrated cooling. On the other hand, these multi-layer ceramic capacitors are also used at ambient environmental temperatures down to −20° C. or lower, for example, in areas having cold climates during winter. In this manner, since multi-layer ceramic capacitors are used over a wide temperature range, they are required to have flat temperature characteristics.
Moreover, dielectric ceramic compositions have recently required to be able to be fired in reducing atmospheres so as to allow the use of base metals such as Ni as well as expensive precious metals such as Pd, Au or Ag in the internal electrodes of multi-layer ceramic capacitors.
Various dielectric ceramic compositions have been developed in response to these requirements (see Japanese Unexamined Patent Publications Nos. 2000-154057, 2001-192264 and 2002-255639). Japanese Unexamined Patent Publication No. 2000-154057 proposes a dielectric ceramic composition at least having a main component in the form of BaTiO3, a first sub-component containing at least one selected from the group consisting of MgO, CaO, BaO, SrO and Cr2O3, a second sub-component represented by (Ba,Ca)xSiO2+x (wherein, x=0.8 to 1.2), a third sub-component containing at least one selected from the group consisting of V2O5, MoO3 and WO3, and a fourth sub-component containing an oxide of R1 (wherein, R1 is at least one selected from the group consisting of Sc, Er, Tm, Yb and Lu); wherein, the ratio of each sub-component to 100 moles of the main component in the form of BaTiO3 is 0.1 to 3 moles for the first sub-component, 2 to 10 moles for the second sub-component, 0.01 to 0.5 moles for the third sub-component and 0.5 to 7 moles for the fourth sub-component (provided that, the number of moles of the fourth sub-component is the ratio of R1 alone).
Japanese Unexamined Patent Publication No. 2001-192264 proposes a dielectric ceramic composition at least having a main component containing barium titanate, a first sub-component containing at least one selected from the group consisting of MgO, CaO, BaO, SrO and Cr2O3, a second sub-component containing silicon oxide as a main component thereof, a third sub-component containing at least one selected from the group consisting of V2O5, MoO3 and WO3, a fourth sub-component containing an oxide of R1 (wherein R1 is at least one selected from the group consisting of Sc, Er, Tm, Yb and Lu), and a fifth sub-component containing CaZrO3 or CaO+ZrO2; wherein, the ratio of each component to 100 moles of the main component containing barium titanate is 0.1 to 3 moles for the first sub-component, 2 to 10 moles for the second sub-component, 0.01 to 0.5 moles for the third sub-component, 0.5 to 7 moles for the fourth sub-component (provided that the number of moles of the fourth sub-component is the ratio of R1 alone), and 0<fifth sub-component≦5 moles for the fifth sub-component.
Japanese Unexamined Patent Publication No. 2002-255639 proposes a dielectric ceramic composition having a main component containing barium titanate, a first sub-component containing an oxide of AE (wherein, AE is at least one selected from the group consisting of Mg, Ca, Ba and Sr), and a second sub-component containing an oxide of R (wherein, R is at least one selected from the group consisting of Y, Dy, Ho and Er); wherein, the ratio of each component to 100 moles of the main component is 0 moles<first sub-component<0.1 moles for the first sub-component, and 1 mole<second sub-component<7 moles for the second sub-component.
However, these dielectric ceramic compositions required further improvement with respect to low dielectric constant, and with respect to dielectric characteristics in particular.